This invention relates generally to components and the method of manufacturing of hollow reflective tubes, and specifically relates to reflective tubes used as integrators and/or angle converters for illumination systems.
Some optical illumination systems benefit from the use of a spatial and/or an angular beam reformatting element to reformat the spatially dependent and/or the angular dependent intensity distribution of a light beam. For example, U.S. Pat. No. 5,625,738 to Magarill describes the use of a straight or symmetrically tapered, hollow, light transmitting tunnel with a rectangular input and output cross sectional shape as an optical element to increase the spatially dependent illumination uniformity of a light valve in a projection display system. European Pat. No. 00734183/EO B1, to Chiu et al. notes that xe2x80x9ctypical illumination schemes usually produce non-uniform illumination on the light valves resulting in poor intensity uniformity . . . xe2x80x9d and teaches a light tunnel comprised of four mirrors assembled to form a hollow rectangular tunnel. U.S. Pat. No. 5,842,767 Rizkin et al. describes another use of a symmetrically tapered hollow cone as an angle converter element to increase the coupling efficiency of an elliptical reflector lamp to a large, round fiber optic bundle input area. While these and other patents describe the use of hollow reflective tubes as integrators and/or angle converters, they don""t describe, in general, a preferred manufacturing method.
The present invention is related to U.S. Pat. No. 6,356,700 of one of the authors of this invention (Strobl) which utilizes, among other things, asymmetrically stretched, hollow anamorphic reflective tubes as integrators and/or angle converter elements to increase the delivery efficiency of an etendue efficient Minimal Light Engine (lamp reflector module) having an asymmetric angular dependent energy distribution in its exit beam that is optically coupled to a light valve or fiber optic light guide. With the emerging large volume market for light valve containing projection display systems for the home entertainment market, there is a need to be able to produce a wide variety of differently shaped, highly reflective rectangular tubes in high volume and at low cost, for use as integrators and angle converters.
When hollow rectangular tubes are manufactured for light beam integrator and/or angle converter applications, the usual prior art method is (1) to manufacture a large sheet of mirror-surfaced material (reflective material), and then (2) to cut or break the reflective material into four suitably sized rectangular sub-components, (3) to assemble these sub-components into a rectangular shaped tube and (4) to glue the four assembled sub-components together to form a permanent and rigid reflective rectangular tube. When a focused light beam is transmitted through such a device, repeated multiple light reflections cause an integration (beam homogenization) of the spatially dependent light intensity distribution. When the four sub-components are assembled in a non-parallel manner, for example as 1-dimensional or as a 2-dimensional rectangular taper, the angular dependent intensity distribution of the incoming focused beam gets modified. In this case, the reflective tube has, beside a spatial beam intensity integration function, also an angle converter function.
The process of cutting or breaking the reflective sheets into the respective rectangular sub-components and their subsequent assembly into a rectangular tube leads to small edge defects (chips) and/or small areas of separation or cracks between the coating and the substrate. In time, these fault areas can lead to a degradation of significant usable area of the reflective coating surface, resulting in parallel in a significant reduction in transmission performance. The transmission efficiency of such a manufactured reflective tube is further reduced by the size of the total area of the gaps and edge imperfections in the four corners between the four assembled neighboring sub-components. This transmission defect is caused by the above-described traditional sub-component manufacturing process. Additionally, this prior art manufacturing process allows economically viable high volume production of rectangular tubes only with a dimensional tolerance of about 100 xcexcm. While this is only a small dimensional uncertainty, it can lead to significant effective transmission losses for very small rectangular integrators. This is in particular important because the overall shortest dimension of a typical integrator for projection display application is already in the range of 4-5 millimeters. The OEM projection display market anticipates that in the near future, when smaller and lower cost light valves become commercially viable for rear projection display systems, the integrator dimensions will shrink proportionally, thus leading to even higher effective transmission losses.
In addition, inside a projection display light engine, the temperature of such hollow reflective tubes is often elevated. Higher efficiency projection illumination technologies are coming to the market in the coming years. These technologies increase the energy density inside such reflective hollow tubes even further. Since there is always some absorption loss even with the best reflective coatings, this increased energy density loading causes a higher head load on the reflective hollow tube components and materials. This increased head load, if not properly managed can lead to a new long term product defect, where the glue holding the four sub-assemblies together becomes mechanically unstable with time, and the performance of the respective projection device is compromised.
Thus, in order to make mass producible, low cost and high performance, small hollow reflective rectangular tubes possible, a new manufacturing method is needed, that, while still suitable for large-scale production, does not suffer from at least some of the above outlined deficiencies.
Traditionally a thin film Ag (silver) over-coating produces the highest substrate reflectivity enhancement in the visible spectral range over a broad range of incident angles. However, the reflectivity of Ag in the visible spectral range has a poor environmentally dependent performance. This is (1) mainly due to its softness, which can lead easily to coating damage during handling, (2) due to its low temperature stability limit (Ag re-crystallization effects cause a surface roughness increase and reflectivity loss above 100 deg C.), and (3) due to the fact that it corrodes readily if it is exposed to air without protection (sulfur binds with Ag and reduces its reflectivity dramatically), i.e. it""s reflectivity in the blue spectral region drops quickly. For these reasons, it is desirable to overcoat Ag with at least one barrier layer. Such a barrier layer must be cohesive to avoid pits, where corrosion of the Ag could begin, and must be hard, to prevent physical damage to the Ag.
U.S. Patent No. 6,128,126, to Hohenegger et al. (Hohenegger I) teaches that while various metal oxide coatings may be used for their hardness and resistance to environmental contaminants, the oxide layer can xe2x80x9ccause a degradation of the silverxe2x80x9d. Hohenegger I mentions various methods to overcome this, such as first covering the Ag layer with further metallic layers to form a barrier between the Ag and the oxide. However, Hohenegger I teaches away from the use of metal oxides and in particular from TiO2 layers stating xe2x80x9cThe solutions attempted in the prior art described above, which suggest packing the Ag containing layer with a metal or a hypostoichiometric oxide layer, fail since as a rule these do not meet the optical specification in any case, at least not with very high reflection values in the visible spectral range at 0-45 deg incident angles.xe2x80x9d U.S. Pat. Nos. 5,751,474 and 5,548,440 to Hohenegger et al. (Hohenegger II and III) while utilizing Ag for the mirror and silicon dioxide and titanium in the barrier layer, teach titanium use only in the form of oxynitrides and not oxides.
U.S. Pat. Nos. 6,128,126, 5,751,474, and 5,548,440 to Hohenegger et al. (collectively Hohenegger) which for brevity are incorporated herein by reference, collectively teach compositions utilizing zinc sulfide as a nucleation layer for forming the Ag reflecting layer on the base substrate and also as an outer protective and high index material layer. Hohenegger also teaches the use of magnesium fluoride or silicon dioxide as barrier and low index material layers. Hohenegger further teaches copper as an additive to the Ag for the purpose of increasing its environmental performance.
The present invention, in contrast to Hohenegger, achieves the very high reflection values of environmentally stable Ag coatings described by Hohenegger, even when substituting the recommended ZnS material with a metal oxide material (Ta2O5, TiO2, ZrO2, etc.), which has been deposited with an ion assisted, e-beam thin film vacuum deposition process.
It is therefore an objective of this invention to provide a method for manufacturing hollow reflective tubes for use as integrators and/or angle converters in illumination systems and in particular for projection display and for fiber optic illumination systems.
It is another objective of this invention to provide a method for high volume capable, low cost manufacturing of hollow integrators and/or angle converters.
It is still another objective of this invention to provide a method for manufacturing sub-components of hollow integrators and/or angle converters.
It is still another objective of this invention to manufacture sub-components which have a continuous reflective coating applied, such that this coating is not fractured during any manufacturing steps near any edges of the optical usable surface area.
It is still a further objective of this invention to facilitate the low cost building of complex shapes, such as two-stage integrators and/or angle converters having a high usable light transmission performance.
It is still another objective of this invention to build more thermally stable reflective tubes that can handle a higher energy load.
It is still a further objective of this invention to provide additional features to each respective sub-component to facilitate inter sub-component alignment and reflective tube to illumination system alignment.
It is still another objective of this invention to utilize a metal oxide (Ta2O5, TiO2, ZrO2, etc.) or ZnS as a high index material, and SiO2 or MgF2 (BaF2, YF3, etc.) as a low index thin film material to enhance and/or environmentally protect thin film Ag coatings on respective sub-component substrate surfaces.
By reviewing and considering the drawings and descriptions further objects and advantages of the present invention will be apparent.
The present invention is based on the realization that the manufacturing process of hollow, highly reflective tubes for integrator and/or angle converter applications in illumination systems is improved if at least some of the features described below are contained in the respective manufacturing process: (1) There should be as few different sub-components as possible, preferably having only two optically functional flat sides connected with each other, (2) the reflectivity enhancing production method of the various surfaces of the respective sub-components should ideally be made in a substantially uniform manner, (3) multiple individual sub-components should be manufacturable and able to be handled as a single unit and should only be separated into individual sub-components after the respective inside surface reflectivity enhancing process is completed and before their final assembly into the desired reflective tube shape, (4) there should preferably be a way to add (deposit, glue, bond, etc.) a highly reflective surface layer on the inside of optically functional surfaces of the respective sub-component in a low cost way, and (5) there should be no edge damaging processing step near the functional surfaces edges after the respective reflectivity enhancing manufacturing process steps, in order to maximize the environmental stability of each sub-component, i.e., to minimize their potential reflectivity degradation over a long time period.
The present invention describes a method of manufacture of hollow reflective tubes out of sub-components that are designed and manufactured in such a manner that they allow precise and low cost assembly into the respective reflective hollow tubes to precise mechanical tolerances, for use as integrators and/or angle converters. These sub-components preferably are xe2x80x9cLxe2x80x9d-shaped and optionally include suitable alignment and/or mounting features that facilitate sub-component alignment with respect to each other and/or optionally facilitate the alignment of the reflective tubes to a respective illumination system.
The present invention also describes several preferred manufacturing methods including molding of the respective sub-components and the application of a highly reflective coating onto the optically functional inside surfaces of the respective sub-components in such a manner that each functional surface gets a substantially similar coating deposited. Optionally, the specular reflectivity (brilliance) of each optically functional surface is enhanced by the application of a surface enhancement layer (base coating) whose purpose is primarily to reduce the surface roughness of the substrate surface, and optionally to facilitate adhesion and/or temperature cycling of the final component.
The preferred method of manufacturing the desired reflective tube is then a simple assembly process of such prepared sub-components facilitated by the design of the respective sub-components, which may include optional self-alignment features and/or system alignment features. Any glue that may be used to bond multiple sub-components together preferably now has only a bonding and does not include a structural function, thus lessening the device""s performance sensitivity to an increased heat load.
Preferably, the number of components needed to build a hollow tube is kept to a minimum and all the sub-components are substantially symmetrical and/or identical. Often one of the symmetry planes of the desired reflective tube is used to decompose the target shape into manufacturable sub-components. In general, production throughput, parts costs, reflectivity specs, environmental stability and heat load resistance dictate the optimum design solution of the respective sub-component shapes together with the process constraints of the chosen reflectivity enhancing manufacturing process.
A preferable method of manufacturing the respective sub-components of this patent is injection, transfer or compression molding of high temperature capable glass fiber-filled plastic resins (glass filled plastics). Preferably, the resin is chosen such that the final sub-component is mechanically stable over the desired temperature range dictated by the application. Thermoplastic and thermosetting materials that don""t flow or move when exposed to temperatures  greater than 100 C are therefore preferred. The inside surface of these sub-components is then preferably coated with a base coating as a specular reflectivity enhancing and/or adhesion promoting under-layer, i.e., a scatter reducing film.
One of the preferred manufacturing processes enables the usage of multi-cavity forming tools. This in turn enables the manufacturing in one step of multiple sub-component substrates that are mechanically connected as one unit and as such facilitate economical cleaning and handling during the various steps needed to add the desired reflectivity enhancing surface coatings. Before the final assembly of the sub-components into the reflective tube, the individual sub-components can then simply be separated (for example broken off or sawed apart) from the multi-unit part and assembled together without risk of damaging the reflective coating near any edges of any functional surfaces.
Another preferred embodiment of the present invention describes the usage of a low temperature, ion-assisted, e-beam thin film deposition process, allowing the utilization of, among other things, plastic substrates and lower temperature surface enhancement layers, and prevents degradation of the Ag layer during the coating process. This method also enables the utilization of metal oxide material like Ta2O5 or TiO2 as high index materials, and SiO2and MgF2 as low index material to enhance the reflectivity and environmental stability of highly reflective Ag films.
A preferred method of mounting the respective sub-components in a vacuum deposition chamber, to obtain uniform coating thickness depositions on all respective optically functional surfaces, is also presented in the present patent application.